Engines are bulletproof in those bikes except for one year they had a recall on intake valves ('06 I believe). They are a little down on power compared to the other 250f's and they don't respond as well to power mods but they are easily the most reliable engine in the class. If you are buying used look for an '06 or newer since they have the aluminum frame, 2010-11 frames are even better but pricier obviously. Try to find one that hasn't been raced and you really can't go wrong.